Stevia is a genus of about 240 species of herbs and shrubs in the sunflower family (Asteraceae), native to subtropical and tropical South America and Central America.
The species Stevia rebaudiana Bertoni, commonly known as sweet leaf, sugarleaf, or simply stevia, is widely grown for its sweet leaves. The leaves have traditionally been used as a sweetener. Steviosides and rebaudiosides are the major constituents of glycosides found in the leaves of the stevia plant.
Over 100 phytochemicals have been discovered in stevia. It is rich in terpenes and flavonoids. Of these eight glycosides, stevioside is considered the sweetest and has been tested to be approximately 300 times sweeter than sugar. Stevioside, comprising 6-18% of the stevia leaf, is also the most prevalent glycoside in the leaf. Other sweet constituents include steviolbioside, rebaudiosides A-E, and dulcoside A.
The main plant chemicals in stevia include: apigenin, austroinulin, avicularin, beta-sitosterol, caffeic acid, campesterol, caryophyllene, centaureidin, chlorogenic acid, chlorophyll, cosmosiin, cynaroside, daucosterol, diterpene glycosides, dulcosides A-B, foeniculin, formic acid, gibberellic acid, gibberellin, indole-3-acetonitrile, isoquercitrin, isosteviol, jhanol, kaempferol, kaurene, lupeol, luteolin, polystachoside, quercetin, quercitrin, rebaudioside A-F, scopoletin, sterebin A-H, steviol, steviolbioside, steviolmonoside, stevioside, stevioside a-3, stigmasterol, umbelliferone, and xanthophylls.
Stevia extracts generally contain a high percentage of the glycosides of the diterpene steviol. The leaves of stevia rebaudiana contain 10 different steviol glycosides. Steviol glycosides are considered high intensity sweeteners (about 250-300 times that of sucrose) and have been used for several years in a number of countries as a sweetener for a range of food products. Stevioside and rebaudioside A are the principal sweetening compounds and generally accompanied by smaller amounts of other steviol glycosides. The taste quality of rebaudioside A is better than stevioside, because of increased sweetness and decreased bitterness (Phytochemistry 68, 2007, 1855-1863).
The structures and chemical abstract service registry numbers for steviol and its glycosides that are the main sweetening agents of the additive steviol glycosides are shown below:
 CompoundnameC.A.S. No.R1R21Steviol  471-80-7HH2Steviolbioside 41093-60-1Hβ-Glc-β-Glc(2→1)3Stevioside 57817-89-7β-Glcβ-Glc-β-Glc(2→1)4Rebaudioside  58543-16-1β-Glcβ-Glc-β-Glc(2→1)A|β-Glc(3→1)5Rebaudioside  58543-17-2Hβ-Glc-β-Glc(2→1)B|β-Glc(3→1)6Rebaudioside  63550-99-2β-Glcβ-Glc-β-Rha(2→1)C|β-Glc(3→1)7Rebaudioside  63279-13-0β-Glc-β-Glc(2→1)β-Glc-β-Glc(2→1)D|β-Glc(3→1)8Rebaudioside  63279-14-1β-Glc-β-Glc(2→1)β-Glc-β-Glc(2→1)E9Rebaudioside 438045-89-7β-Glcβ-Glc-β-Xyl(2→1)F|β-Glc(3→1)10Rubusoside 63849-39-4β-Glcβ-Glc11Dulcoside A 64432-06-0β-Glcβ-Glc-α-Rha(2→1)
Steviol glycoside preparations are generally white to light yellow powders that are freely soluble in water and ethanol. The powders can be odorless or have a slight characteristic odor. Aqueous solutions are 200 to 300 times sweeter than sucrose under identical conditions. With its extracts having up to 300 times the sweetness of sugar, stevia has garnered attention with the rise in demand for low-carbohydrate, low-sugar food alternatives.
Medical research has also shown possible benefits of stevia in treating obesity and high blood pressure. Because stevia has a negligible effect on blood glucose, it is attractive as a natural sweetener to people on carbohydrate-controlled diets.
As a sweetener and sugar substitute, rebaudioside A has a slower onset and longer duration than that of sugar, and be deemed very close to sucrose, although some of its extracts may have a bitter or licorice-like aftertaste at high concentrations. All steviol glycosides are bitter, some in less degree and some in greater degree.
Therefore, a need exists for a sweetener that overcomes one or more of the current disadvantages noted above.